In order to mount a shower curtain for a shower, it is necessary to first secure a shower curtain rod between two of the walls which define the shower area. In some cases, the shower curtain rod can be a fixed length tube permanently mounted between the walls. The problem with a design of this type, is that the fixed length rod must be cut exactly to the dimensions of the shower space. The rod is then fitted into a pair of rod mounts with each mount secured to a wall. Should it be necessary to adjust the height of the shower rod, it would be necessary to revise the rod mounts, repair the wall where the fixed rod was mounted, and secure the mounts to the new location. It may also be necessary to cut a new fixed length rod, if the dimensions of the walls vary between the old and new positions.
Adjustable, pressure fitted shower rods solve the problems associated with a fixed length rod. In such a shower rod, the length of the shower rod is adjustable within a range. Tightening the rod in the space between the two walls maintains a tight fix, sufficient to securely hold a shower curtain without slipping. These designs require a large number of rotations of the threaded rods to extend the rods to the typical four to six foot wall spans.
Same designs, such as those shown in U.S. Pat. No. 670,585 to Fouler, U.S. Pat. No. 856,316 to Thirston and U.S. Pat. No. 1,548,053 to Mead use a combination of a threaded rod fitted within another threaded rod and a biasing spring to maintain tension as the rod is extended to fit between walls.
Other designs such as those shown in U.S. Pat. No. 2,919,134 to Zero, U.S. Pat. No. 3,521,758 to Gylfoyle and U.S. Pat. No. 704,403 to Phil show threaded rods which do not use a biasing spring to maintain force.
The designs using a spring, aside from having the additional manufacturing cost and added complexity of having a spring component, suffer from the difficulty of having to provide sufficient force to compress this spring when adjusting the rod. Further, there is always the possibility of the rod and spring becoming entangled or the spring popping out of the rod during assembly/disassembly.
In the designs which do not use a spring, the threaded fittings must be sufficiently tight to maintain enough force to keep the rod in place. In these designs, it is possible for the threads to loosen, with the rod slipping or falling. With the light weight materials typically used in the manufacture of shower curtain rods (and curtain rods) some form of biasing mechanism is desirable to maintain a tight fit and prevent slippage of the rod.